Sour Grapes harmony (Bakovic, 2000; Wilson, 2006) is an unattested phonological pattern in which disharmonic sequences of vowels are generally not allowed in surface forms but are licensed when a segment that blocks the pattern appears to one side of the disharmonic sequence (Bakovic, 2000; Wilson, 2006). Typically, explanations for why Sour Grapes patterns are unattested seek to categorically limit phonological grammars so that they cannot represent them—either by revising the set of constraints used to capture harmony (e.g., Wilson, 2006; McCarthy, 2011) or by focusing on the formal complexity of Sour Grapes and working toward a theory of phonology that categorically forbids any pattern that complex (e.g., Heinz, 2018; Smith & O'Hara, 2019; Lamont, 2019). Here, evidence is presented from agent based simulations for an alternative explanation: that the learnability of Sour Grapes causes it to be less diachronically stable than more standard harmony patterns, which could lead to its typological absence.